1. Field of the Invention
The present invention relates to a printed board which enables superior packaging of an electronic component to be performed, and to a portable electronic device which uses this printed board.
Priority is claimed on Japanese Patent Application No. 2008-046761, filed. Feb. 27, 2008, the contents of which are incorporated herein by reference.
2. Description of Related Art
As is commonly known, BGA (Ball Grid Array) and CSP (Chip Size Packages) are widely used as packages to house semiconductor chips. These BGA and CSP (abbreviated below to “BGA and the like”) are packages which have small ball-shaped electrodes (i.e., bumps) made of solder which are arranged in a grid layout on a bottom surface thereof as connection terminals which electrically connect the printed board to semiconductor chips which are housed inside the packages. In this type of BGA and the like, an area between the bottom surface thereof which faces the printed board and the printed board is filled with an underfill material (i.e., an epoxy resin) which serves as an adhesive material. This underfill material is then heat-cured so as to become more firmly fixed on the printed board. This is in order to improve connection reliability in the face of thermal stress such as heat cycles and the like, and to improve connection reliability in the face of physical stress such as shock and bending and the like. However, because this underfill material is made to permeate into the gaps between the package and the printed board by means of a capillary phenomenon and is then heat-cured, it also permeates to the periphery of adjacent IC. Moreover, if too much underfill is used, or if the locations where it is injected are unsuitable, then the underfill material flows out from between the BGA and the like and the printed board. This overflowing underfill material adheres to screw holes and to mounting surfaces of electronic component protective components provided in the printed board and the like, so that the mounting accuracy of these components deteriorates markedly.
In Japanese Unexamined Patent Application, First Publication, No. 2001-53411 (JP 2001-53411A), a method is disclosed in which a BGA is packaged while this type of overflow of the underfill material is prevented. Namely, a method is disclosed in which a through hole via is provided in a printed board so as to correspond to the packaging location of the BGA, and after the BGA has been positioned so as to cover this through hole via, and after the bumps and the semiconductor pattern on the printed board have been electrically connected, underfill material is injected through the through hole via so as to fill the space between the BGA and the printed board. Namely, the underfill material which is injected through the through hole via in the printed board fills this space while spreading out radially in the planar direction of the board, so that the underfill material is prevented from overflowing.
However, in the conventional technology, because the through hole via is provided in a bottom surface of the printed board, the number of connection terminals formed by the ball-shaped electrodes is reduced corresponding to the size of the surface area taken up by the through hole via, so that the problem arises that restrictions are placed on the number of possible electrical connections between electronic components and the printed board.
The present invention was conceived in view of the above described circumstances, and it is an object thereof to provide a printed board and a portable electronic device which uses this printed board that, without placing any restrictions on electrical connections between electronic components and a printed board, make it possible to secure superior mounting accuracy while preventing underfill material which has overflowed from between a package and a printed board becoming adhered to screw holes or mounting surfaces formed on the printed board.